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One-step process for the fabrication of Ti porous compact and its surface modification by environmental-electro-discharge-sintering of spherical Ti powders
Surface & Coatings Technology 200 (2006) 4300 – 4304 www.elsevier.com/locate/surfcoat
One-step process for the fabrication of Ti porous compact and its surface modification by environmental-electro-discharge-sintering of spherical Ti powders Y.B. Ana, N.H. Oha, Y.W. Chuna, D.K. Kima, J.S. Parkb, K.O. Choic, T.G. Eomc, T.H. Byunc, J.Y. Kimd, C.S. Byune, C.Y. Hyunf, P.J. Reucroftg, W.H. Leea,T a
Department of Advanced Materials Engineering, Sejong Bioengineering Research Center, Sejong University, Seoul 143-747, Korea b Department of Metallurgical Engineering, Yonsei University, Seoul, 120-749 Korea c Manufacturing Division, Osstem Co., Ltd., Busan, 611-073 Korea d Department of Materials Engineering, Uiduk University, Kyungbuk 780-713, Korea e Department of Materials Engineering, Hanbat University, Daejeon 305-719 Korea f Department of Materials Engineering, Seoul National University of Technology, Seoul 139-743 Korea g Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY, USA Received 14 November 2004; accepted in revised form 5 February 2005 Available online 30 March 2005
Abstract A single pulse of 1.0 kJ/0.7 g of atomized spherical Ti powders from 300 AF capacitor was applied to produce a porous-surfaced Ti compact by environmental-electro-discharge-sintering (EEDS). A solid core was automatically formed by a discharge in the middle of the compact which is surrounded by a porous layer, which increased the porous compact’s compressive yield strength from 52 to 125 MPa. The surface of the EEDS compact has been instantaneously modified by a discharge into the form of primarily Ti nitride from TiO2. Therefore, EEDS can fabricate a Ti porous-surfaced compact with a solid core and simultaneously modify its surface chemistry in times as short as 122 As. D 2005 Elsevier B.V. All rights reserved. Keywords: Sintering; X-ray photoelectron spectroscopy (XPS); Electro-discharge; Titanium; Surface diffusion
1. Introduction Fabrication of porous and porous-surfaced metal compacts normally involves either plasma-spraying or sintering powders onto a solid substrate [1–3]. A two stage porous compact was fabricated from Ti-6Al-4V powders by Young et al. [4]. The high temperature sintering process employed in their work yielded a porous-surfaced coating with 34% porosity and an average pore size of 125 Am. The poroussurfaced Ti-6Al-4V compacts have been widely used as dental or orthopedic implants since the surface features of
T Corresponding author. Tel.: +82 2 3408 3779; fax: +82 2 3408 3664. E-mail address: [email protected] (W.H. Lee). 0257-8972/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2005.02.127
implant have been changed from smooth to notched surfaces for the promotion of immobilization of the implant in bone by enabling mechanical interlocking between the implant and tissue, leading to faster osseointegration. However, several problems related to the sintering process, such as undesirable strength and microstructural change of the material, have been recognized due to a long exposure to high heats. For example, the solid core and porous portion of the sintered compact exhibited a typical large grained a + h structure. Therefore, highly efficient technique for the consolidation of metal powder in very short time needs to be developed. When the surface of the sintered porous metal compact is needed to be modified on purpose, one of several techniques such as chemical vapor deposition (CVD), sputtering,
Y.B. An et al. / Surface & Coatings Technology 200 (2006) 4300–4304
Capacitors
4301
High vacuum switch MFC
Power supply High voltage probe
Oscilloscope
Computer
High current probe
Vacuum pump Fig. 1. Environmental-electro-discharge-sintering schematic.
evaporating, and gas nitriding processes may be introduced. However, these processes are somewhat complicate, costly, and also time consuming. Therefore, we have first introduced the process of environmental-electro-discharge-sintering (EEDS) for the fabrication of the surface-modified porous Ti compact. Nitrogen environment in the discharge chamber was thus used in order to form titanium nitrides on the surface of compact. A schematic diagram of the process is shown in Fig. 1. Although surface properties of conventional Ti have been frequently examined [5,6], to date the surface characteristics of EEDS porous compact fabricated in a N2 atmosphere have not been reported. Therefore, X-ray photoelectron spectroscopy (XPS) has been employed to examine the surface chemical composition of the porous-surfaced Ti compact fabricated by EEDS.
2. Experimental procedure Atomized titanium spherical powders (Grade II), produced by the rotating electrode process (TLS Technik, Germany), were sieved to yield one particle size class of 150–200 Am. A 0.7 g of powder was vibrated into a quartz tube with an inner diameter of 4.0 mm that had a tungsten
electrode at the bottom. A Cu heat sink tube was placed into the quartz mold. An upper electrode was automatically machined-driven on the top of the powder column followed by applying a load of 10 kg. The discharging chamber was evacuated up to 2 10 2 Torr and then filled with a N2 gas up to 200 Torr. One capacitor bank of 300 AF was charged with 1.0 kJ input energy. The charged capacitor bank instantaneously discharged through the powder column by on/off high vacuum switch which closes the discharge circuit. The voltage and current that the powder column experiences when the circuit is closed are simultaneously picked up by a high voltage probe and a high current probe, respectively. EEDS porous compact obtained from current experimental condition was sliced every 2 mm and their crosssections were examined under an optical microscope. The porous compact without doing any surface treatment after discharge was mounted on the spectrometer probe tip by means of double-sided adhesive tape and examined by XPS. Under current conditions, the full width at half maximum (FWHM) of the Ag 3d5/2 peak was 1.1 eV, and the binding energy difference between Ag 3d5/2 and Ag 3d3/2 was 6.0 eV. When the Ag 3d5/2 peak was used as the reference peak, the binding energy of the C 1s peak of adventitious carbon on the standard silver surface was 285
Fig. 2. (a) Typical appearance and (b) cross-section view of EEDS compact.
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Y.B. An et al. / Surface & Coatings Technology 200 (2006) 4300–4304
Fig. 3. Typical optical micrographs of (a) powders in the porous layer and (b) the solid core.
eV. All binding energies were referenced to the C 1s peak to correct for sample charging. Ar+ ion sputtering was carried out up to 1.5 min, resulting that the etching rate was approximately 73 2/min, as determined from a SiO2 standard film.
3. Results and discussion Typical surface appearance and cross-section views of the porous Ti compact after discharge are shown in Fig. 2(a) and (b), respectively, illustrating the porous-surfaced feature. The discharge time was estimated to be about 122 As. A solid core was successfully formed by a discharge in the center of the compact which is surrounded by a porous layer. The solid core is composed of powder particles which were deformed and welded together. The porous layer consists of powder particles which are connected by necks in three dimensions. Fig. 3(a) and (b) show typical optical micrographs of powder particles in the porous layer and the solid core of the compact, respectively. The main phase shown in the micrographs is known to be an alpha prime (aV). aV is a non-equilibrium supersaturated a´ structure produced martensitic transformation from h. Both the solid
O1s O KLL
A.U
Ti2p
C1s N1s
EEDS compact
Table 1 XPS elemental analysis data expressed in terms of atomic concentration
As-received Ti powder 800
700
600
500 400 300 Binding energy (eV)
200
100
core and powder particles in the porous layer showed similar microstructure of cp titanium which was annealed and quenched in the water [7]. The porosity of Ti compact was estimated to be about 36.6% by measuring the compact’s diameter and length. For the compressive strength, the compact was placed on the bottom jig and subjected to load. Under the current experimental condition the estimated compressive yield strength of the compact was about 125 MPa. Survey spectra, as shown in Fig. 4, over the binding energy range 0–800 eV, were used to identify the surface elements present in the EEDS compact and the as-received Ti powder before discharge. To determine the atomic concentration of the elements, quantitative peak analysis was carried out. The resulting data is listed in Table 1 for the EEDS compact. Ti, O and C were the main constituents in the case of as-received powder. However, EEDS compact showed a distinct N 1s peak at about 400 eV. Both the asreceived powders and the EEDS compact were further analyzed by combining Ar+ sputtering with XPS measurements. Although different features such as preferential sputtering, atomic mixing, particle size effects, etc., can affect the etching profiles, similar etching rates of the Ti were expected in the present studies [8,9]. High resolution scans were then used to obtain information regarding the surface chemical state of the materials. Fig. 5 shows narrow scan spectra of the Ti 2p region for the EEDS compact before and after etching, including that for the as-received powders. As-received Ti powder showed a Ti 2p3/2 peak at 458.5 eV, with 5.8 eV splitting between the Ti 2p1/2 and Ti 2p3/2 peaks. Previous results on Ti narrow scan spectra of wrought Ti and Ti alloy show Ti 2p3/2 peak at about 459.2 eV with 5.8 eV splitting between the Ti 2p1/2 and Ti 2p3/2 [10–13]. For Ti4+, as in TiO2, the Ti 2p3/2 peak is at
Element
0
Fig. 4. XPS high resolution spectra of the Ti 2p region for EEDS compact and as-received powders.
C O Ti N
Atomic concentration (%) Before etching
After etching
57.0 25.5 8.4 9.1
10.0 11.1 52.9 26.0
Y.B. An et al. / Surface & Coatings Technology 200 (2006) 4300–4304
adsorbed TiN nitrogen
A.U
A.U
TiN TiNO Ti
TiO2 Ti2O3
etching
4303
etching
before etching
As-received powder 408 406 404 402 400 398 396 394 392 390 388 470
465 460 455 Binding energy (eV)
450
Binding energy (eV)
Fig. 5. XPS high resolution spectra of the Ti 2p region for EEDS compact before and after etching.
about 459.1 eV [8]. Peak shifts for Ti3+(Ti2O3), Ti2+(TiO), and Ti (metal) are approximately 1.7, 3.5, and 5.2 eV, respectively [11,12]. Thus, the surface of as-received Ti powder before discharge is primarily in the form of TiO2. However, the surface of EEDS compact has been changed into mixed Ti oxides and nitrides after discharge. Lightly etched EEDS compact showed a Ti 2p3/2 peak at 454.6 eV, with 5.8 eV splitting between the Ti 2p1/2 and Ti 2p3/2 peaks. Therefore, the surface is primarily in the form of Ti nitrides, such as TiNO and TiN. It can thus be known that the EEDS process can successfully modify the original surface of the as-received powders from TiO2 to Ti nitride in 122 As. This result can be ascribed to EEDS breaking down the oxide film of the as-received Ti powders. Then, the unoxidized Ti surface of the compact subsequently reacted mainly with nitrogen forming Ti nitride during the discharge process [13]. High resolution spectra of the O 1s region for the EEDS compact before and after etching are shown in Fig. 6. The component of about 530 eV can be assigned to oxygen from
C-O-C >C=0 TiO 2 groups groups
A.U
etching
540
538
536
534
532
530
528
526
524
Fig. 7. XPS high resolution spectra of the N 1s region for EEDS compact before and after etching.
the Ti oxides. The broad shoulder extending from 531 to 534 eV consists of two possible types of oxygen such as C– O–C and NCjO groups [14]. After light etching, very small amount of oxygen has been found due to an exposal of nitrogen in the form of Ti nitride. Fig. 7 shows high resolution spectra of the N 1s region for the EEDS compact before and after etching. The maximums at 400.1 and 397.1 eV are identical to the N 1s positions for adsorbed organic nitrogen and nitride, respectively. This indicates the presence of significant amount of nitride and supports assignment of Ti nitride peak to the Ti 2p spectrum. It was therefore concluded that the EEDS of Ti powders can produce a porous-surfaced compact with a successful surface modification in times as short as 122 As.
4. Conclusions Environmental-electro-discharge-sintering (EEDS) in a nitrogen atmosphere was first employed to fabricate a porous-surfaced Ti compact from atomized Ti powders, which was subjected a discharge of 1.0 kJ/0.7 g powder from 300 AF capacitor bank. The solid core was automatically formed in the center of the compact and porous layer consisted of particles connected in three dimensions by necks. EEDS broke the oxide film of as-received powder and then unoxidized Ti surface subsequently reacted with nitrogen, forming primarily Ti nitride during the discharge. Therefore, EEDS of spherical Ti powders successfully produced a porous-surfaced compact, which surface was simultaneously modified into Ti nitride by one-step process in times as short as 122 Asec.
Acknowledgements
Binding energy (eV) Fig. 6. XPS high resolution spectra of the O 1s region for EEDS compact before and after etching.
This work was supported by Korea Research Foundation Grant (KRF-2001-041-E00490).
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Y.B. An et al. / Surface & Coatings Technology 200 (2006) 4300–4304
References [1] K. Asaoka, N. Kuwayama, O. Okuno, I. Miura, J. Biomed. Mater. Res. 19 (1985) 699. [2] S. Yue, R.M. Pillar, G.C. Weatherly, J. Biomed. Mater. Res. 18 (1984) 1043. [3] R.M. Pilliar, R. Vowles, R.F. Williams, J. Biomed. Mater. Res. 21 (1987) 145. [4] F. Young, M. Spector, C. Kresch, J. Biomed. Mater. Res. 13 (1979) 845. [5] J.L. Ong, C.W. Prince, L.C. Lucas, J. Biomed. Mater. Res. 29 (1995) 165. [6] N. Jiang, H.J. Zhang, S.N. Bao, Y.G. Shen, Z.F. Zhou, Phys. Rev. B: Condens. Matter 352 (2004) 118.
[7] M. Donachie, Titanium, A Technical Guide, ASM International, Ohio, 2000, p. 14. [8] J.Y. Kim, P.J. Reucroft, V.R. Pradhan, I. Wender, Fuel Process. Technol. 34 (1993) 207. [9] J.Y. Kim, P.J. Reucroft, M. Taghiei, V.R. Pradhan, I. Wender, Energy Fuels 8 (1994) 886. [10] M. Ask, J. Lausmaa, B. Kasemo, Appl. Surf. Sci. 35 (1989) 283. [11] N.R. Armstrong, R.K. Quinn, Surf. Sci. 67 (1977) 451. [12] W. Gopel, J.A. Anderson, D. Frankel, M. Jaehnig, K. Phillips, J.A. Shaffer, G. Rocker, Surf. Sci. 139 (1984) 333. [13] C.N. Sayers, N.R. Armstrong, Surf. Sci. 77 (1978) 301. [14] D. Georgiev, R. Baird, G. Newas, G. Auner, R. Witte, H. Herfurth, Appl. Surf. Sci. 236 (2004) 71.
One-step process for the fabrication of Ti porous compact and its surface modification by environmental-electro-discharge-sintering of spherical Ti powders Y.B. Ana, N.H. Oha, Y.W. Chuna, D.K. Kima, J.S. Parkb, K.O. Choic, T.G. Eomc, T.H. Byunc, J.Y. Kimd, C.S. Byune, C.Y. Hyunf, P.J. Reucroftg, W.H. Leea,T a
Department of Advanced Materials Engineering, Sejong Bioengineering Research Center, Sejong University, Seoul 143-747, Korea b Department of Metallurgical Engineering, Yonsei University, Seoul, 120-749 Korea c Manufacturing Division, Osstem Co., Ltd., Busan, 611-073 Korea d Department of Materials Engineering, Uiduk University, Kyungbuk 780-713, Korea e Department of Materials Engineering, Hanbat University, Daejeon 305-719 Korea f Department of Materials Engineering, Seoul National University of Technology, Seoul 139-743 Korea g Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY, USA Received 14 November 2004; accepted in revised form 5 February 2005 Available online 30 March 2005
Abstract A single pulse of 1.0 kJ/0.7 g of atomized spherical Ti powders from 300 AF capacitor was applied to produce a porous-surfaced Ti compact by environmental-electro-discharge-sintering (EEDS). A solid core was automatically formed by a discharge in the middle of the compact which is surrounded by a porous layer, which increased the porous compact’s compressive yield strength from 52 to 125 MPa. The surface of the EEDS compact has been instantaneously modified by a discharge into the form of primarily Ti nitride from TiO2. Therefore, EEDS can fabricate a Ti porous-surfaced compact with a solid core and simultaneously modify its surface chemistry in times as short as 122 As. D 2005 Elsevier B.V. All rights reserved. Keywords: Sintering; X-ray photoelectron spectroscopy (XPS); Electro-discharge; Titanium; Surface diffusion
1. Introduction Fabrication of porous and porous-surfaced metal compacts normally involves either plasma-spraying or sintering powders onto a solid substrate [1–3]. A two stage porous compact was fabricated from Ti-6Al-4V powders by Young et al. [4]. The high temperature sintering process employed in their work yielded a porous-surfaced coating with 34% porosity and an average pore size of 125 Am. The poroussurfaced Ti-6Al-4V compacts have been widely used as dental or orthopedic implants since the surface features of
T Corresponding author. Tel.: +82 2 3408 3779; fax: +82 2 3408 3664. E-mail address: [email protected] (W.H. Lee). 0257-8972/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2005.02.127
implant have been changed from smooth to notched surfaces for the promotion of immobilization of the implant in bone by enabling mechanical interlocking between the implant and tissue, leading to faster osseointegration. However, several problems related to the sintering process, such as undesirable strength and microstructural change of the material, have been recognized due to a long exposure to high heats. For example, the solid core and porous portion of the sintered compact exhibited a typical large grained a + h structure. Therefore, highly efficient technique for the consolidation of metal powder in very short time needs to be developed. When the surface of the sintered porous metal compact is needed to be modified on purpose, one of several techniques such as chemical vapor deposition (CVD), sputtering,
Y.B. An et al. / Surface & Coatings Technology 200 (2006) 4300–4304
Capacitors
4301
High vacuum switch MFC
Power supply High voltage probe
Oscilloscope
Computer
High current probe
Vacuum pump Fig. 1. Environmental-electro-discharge-sintering schematic.
evaporating, and gas nitriding processes may be introduced. However, these processes are somewhat complicate, costly, and also time consuming. Therefore, we have first introduced the process of environmental-electro-discharge-sintering (EEDS) for the fabrication of the surface-modified porous Ti compact. Nitrogen environment in the discharge chamber was thus used in order to form titanium nitrides on the surface of compact. A schematic diagram of the process is shown in Fig. 1. Although surface properties of conventional Ti have been frequently examined [5,6], to date the surface characteristics of EEDS porous compact fabricated in a N2 atmosphere have not been reported. Therefore, X-ray photoelectron spectroscopy (XPS) has been employed to examine the surface chemical composition of the porous-surfaced Ti compact fabricated by EEDS.
2. Experimental procedure Atomized titanium spherical powders (Grade II), produced by the rotating electrode process (TLS Technik, Germany), were sieved to yield one particle size class of 150–200 Am. A 0.7 g of powder was vibrated into a quartz tube with an inner diameter of 4.0 mm that had a tungsten
electrode at the bottom. A Cu heat sink tube was placed into the quartz mold. An upper electrode was automatically machined-driven on the top of the powder column followed by applying a load of 10 kg. The discharging chamber was evacuated up to 2 10 2 Torr and then filled with a N2 gas up to 200 Torr. One capacitor bank of 300 AF was charged with 1.0 kJ input energy. The charged capacitor bank instantaneously discharged through the powder column by on/off high vacuum switch which closes the discharge circuit. The voltage and current that the powder column experiences when the circuit is closed are simultaneously picked up by a high voltage probe and a high current probe, respectively. EEDS porous compact obtained from current experimental condition was sliced every 2 mm and their crosssections were examined under an optical microscope. The porous compact without doing any surface treatment after discharge was mounted on the spectrometer probe tip by means of double-sided adhesive tape and examined by XPS. Under current conditions, the full width at half maximum (FWHM) of the Ag 3d5/2 peak was 1.1 eV, and the binding energy difference between Ag 3d5/2 and Ag 3d3/2 was 6.0 eV. When the Ag 3d5/2 peak was used as the reference peak, the binding energy of the C 1s peak of adventitious carbon on the standard silver surface was 285
Fig. 2. (a) Typical appearance and (b) cross-section view of EEDS compact.
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Y.B. An et al. / Surface & Coatings Technology 200 (2006) 4300–4304
Fig. 3. Typical optical micrographs of (a) powders in the porous layer and (b) the solid core.
eV. All binding energies were referenced to the C 1s peak to correct for sample charging. Ar+ ion sputtering was carried out up to 1.5 min, resulting that the etching rate was approximately 73 2/min, as determined from a SiO2 standard film.
3. Results and discussion Typical surface appearance and cross-section views of the porous Ti compact after discharge are shown in Fig. 2(a) and (b), respectively, illustrating the porous-surfaced feature. The discharge time was estimated to be about 122 As. A solid core was successfully formed by a discharge in the center of the compact which is surrounded by a porous layer. The solid core is composed of powder particles which were deformed and welded together. The porous layer consists of powder particles which are connected by necks in three dimensions. Fig. 3(a) and (b) show typical optical micrographs of powder particles in the porous layer and the solid core of the compact, respectively. The main phase shown in the micrographs is known to be an alpha prime (aV). aV is a non-equilibrium supersaturated a´ structure produced martensitic transformation from h. Both the solid
O1s O KLL
A.U
Ti2p
C1s N1s
EEDS compact
Table 1 XPS elemental analysis data expressed in terms of atomic concentration
As-received Ti powder 800
700
600
500 400 300 Binding energy (eV)
200
100
core and powder particles in the porous layer showed similar microstructure of cp titanium which was annealed and quenched in the water [7]. The porosity of Ti compact was estimated to be about 36.6% by measuring the compact’s diameter and length. For the compressive strength, the compact was placed on the bottom jig and subjected to load. Under the current experimental condition the estimated compressive yield strength of the compact was about 125 MPa. Survey spectra, as shown in Fig. 4, over the binding energy range 0–800 eV, were used to identify the surface elements present in the EEDS compact and the as-received Ti powder before discharge. To determine the atomic concentration of the elements, quantitative peak analysis was carried out. The resulting data is listed in Table 1 for the EEDS compact. Ti, O and C were the main constituents in the case of as-received powder. However, EEDS compact showed a distinct N 1s peak at about 400 eV. Both the asreceived powders and the EEDS compact were further analyzed by combining Ar+ sputtering with XPS measurements. Although different features such as preferential sputtering, atomic mixing, particle size effects, etc., can affect the etching profiles, similar etching rates of the Ti were expected in the present studies [8,9]. High resolution scans were then used to obtain information regarding the surface chemical state of the materials. Fig. 5 shows narrow scan spectra of the Ti 2p region for the EEDS compact before and after etching, including that for the as-received powders. As-received Ti powder showed a Ti 2p3/2 peak at 458.5 eV, with 5.8 eV splitting between the Ti 2p1/2 and Ti 2p3/2 peaks. Previous results on Ti narrow scan spectra of wrought Ti and Ti alloy show Ti 2p3/2 peak at about 459.2 eV with 5.8 eV splitting between the Ti 2p1/2 and Ti 2p3/2 [10–13]. For Ti4+, as in TiO2, the Ti 2p3/2 peak is at
Element
0
Fig. 4. XPS high resolution spectra of the Ti 2p region for EEDS compact and as-received powders.
C O Ti N
Atomic concentration (%) Before etching
After etching
57.0 25.5 8.4 9.1
10.0 11.1 52.9 26.0
Y.B. An et al. / Surface & Coatings Technology 200 (2006) 4300–4304
adsorbed TiN nitrogen
A.U
A.U
TiN TiNO Ti
TiO2 Ti2O3
etching
4303
etching
before etching
As-received powder 408 406 404 402 400 398 396 394 392 390 388 470
465 460 455 Binding energy (eV)
450
Binding energy (eV)
Fig. 5. XPS high resolution spectra of the Ti 2p region for EEDS compact before and after etching.
about 459.1 eV [8]. Peak shifts for Ti3+(Ti2O3), Ti2+(TiO), and Ti (metal) are approximately 1.7, 3.5, and 5.2 eV, respectively [11,12]. Thus, the surface of as-received Ti powder before discharge is primarily in the form of TiO2. However, the surface of EEDS compact has been changed into mixed Ti oxides and nitrides after discharge. Lightly etched EEDS compact showed a Ti 2p3/2 peak at 454.6 eV, with 5.8 eV splitting between the Ti 2p1/2 and Ti 2p3/2 peaks. Therefore, the surface is primarily in the form of Ti nitrides, such as TiNO and TiN. It can thus be known that the EEDS process can successfully modify the original surface of the as-received powders from TiO2 to Ti nitride in 122 As. This result can be ascribed to EEDS breaking down the oxide film of the as-received Ti powders. Then, the unoxidized Ti surface of the compact subsequently reacted mainly with nitrogen forming Ti nitride during the discharge process [13]. High resolution spectra of the O 1s region for the EEDS compact before and after etching are shown in Fig. 6. The component of about 530 eV can be assigned to oxygen from
C-O-C >C=0 TiO 2 groups groups
A.U
etching
540
538
536
534
532
530
528
526
524
Fig. 7. XPS high resolution spectra of the N 1s region for EEDS compact before and after etching.
the Ti oxides. The broad shoulder extending from 531 to 534 eV consists of two possible types of oxygen such as C– O–C and NCjO groups [14]. After light etching, very small amount of oxygen has been found due to an exposal of nitrogen in the form of Ti nitride. Fig. 7 shows high resolution spectra of the N 1s region for the EEDS compact before and after etching. The maximums at 400.1 and 397.1 eV are identical to the N 1s positions for adsorbed organic nitrogen and nitride, respectively. This indicates the presence of significant amount of nitride and supports assignment of Ti nitride peak to the Ti 2p spectrum. It was therefore concluded that the EEDS of Ti powders can produce a porous-surfaced compact with a successful surface modification in times as short as 122 As.
4. Conclusions Environmental-electro-discharge-sintering (EEDS) in a nitrogen atmosphere was first employed to fabricate a porous-surfaced Ti compact from atomized Ti powders, which was subjected a discharge of 1.0 kJ/0.7 g powder from 300 AF capacitor bank. The solid core was automatically formed in the center of the compact and porous layer consisted of particles connected in three dimensions by necks. EEDS broke the oxide film of as-received powder and then unoxidized Ti surface subsequently reacted with nitrogen, forming primarily Ti nitride during the discharge. Therefore, EEDS of spherical Ti powders successfully produced a porous-surfaced compact, which surface was simultaneously modified into Ti nitride by one-step process in times as short as 122 Asec.
Acknowledgements
Binding energy (eV) Fig. 6. XPS high resolution spectra of the O 1s region for EEDS compact before and after etching.
This work was supported by Korea Research Foundation Grant (KRF-2001-041-E00490).
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Y.B. An et al. / Surface & Coatings Technology 200 (2006) 4300–4304
References [1] K. Asaoka, N. Kuwayama, O. Okuno, I. Miura, J. Biomed. Mater. Res. 19 (1985) 699. [2] S. Yue, R.M. Pillar, G.C. Weatherly, J. Biomed. Mater. Res. 18 (1984) 1043. [3] R.M. Pilliar, R. Vowles, R.F. Williams, J. Biomed. Mater. Res. 21 (1987) 145. [4] F. Young, M. Spector, C. Kresch, J. Biomed. Mater. Res. 13 (1979) 845. [5] J.L. Ong, C.W. Prince, L.C. Lucas, J. Biomed. Mater. Res. 29 (1995) 165. [6] N. Jiang, H.J. Zhang, S.N. Bao, Y.G. Shen, Z.F. Zhou, Phys. Rev. B: Condens. Matter 352 (2004) 118.
[7] M. Donachie, Titanium, A Technical Guide, ASM International, Ohio, 2000, p. 14. [8] J.Y. Kim, P.J. Reucroft, V.R. Pradhan, I. Wender, Fuel Process. Technol. 34 (1993) 207. [9] J.Y. Kim, P.J. Reucroft, M. Taghiei, V.R. Pradhan, I. Wender, Energy Fuels 8 (1994) 886. [10] M. Ask, J. Lausmaa, B. Kasemo, Appl. Surf. Sci. 35 (1989) 283. [11] N.R. Armstrong, R.K. Quinn, Surf. Sci. 67 (1977) 451. [12] W. Gopel, J.A. Anderson, D. Frankel, M. Jaehnig, K. Phillips, J.A. Shaffer, G. Rocker, Surf. Sci. 139 (1984) 333. [13] C.N. Sayers, N.R. Armstrong, Surf. Sci. 77 (1978) 301. [14] D. Georgiev, R. Baird, G. Newas, G. Auner, R. Witte, H. Herfurth, Appl. Surf. Sci. 236 (2004) 71.